Surrounding us in everyday life, sensors play a crucial role in various applications, from everyday household devices like garage lights and smoke detectors to advanced scientific instruments. One particular type of sensor, known as quantum sensors, utilizes the unique properties of atoms to sense and measure the surrounding environment. For instance, when exposed to a magnetic field, an atom's spin, similar to the poles of a magnet, undergoes a change. Magnetic field sensors based on quantum principles find applications in fields like biomedical appliances and research on quantum materials such as superconductors.

Figure 1. Quantum sensor nanoarray.

Figure 1 shows (a) Boron vacancy defect in hexagonal boron nitride. The vacancy acts as an atom-sized quantum sensor for magnetic field measurements. The magnetic field-sensitive quantum sensor behaves like a nano-sized “magnetic needle”. (b) Photoluminescence of a quantum sensor nanoarray. By analyzing the change in the photoluminescence intensity in response to microwaves, the researchers measured the magnetic field at each sensor spot. Many quantum sensors are generated at each bright spot.

Assistant Professor Kento Sasaki from the University of Tokyo shares the researchers' ambition: "Using such an unprecedented sensor, we want to observe a microscopic world that no one has ever seen."

The challenge has always been to arrange atoms in a precise manner, enabling the development of stable quantum sensors in close proximity to specific targets like wires and disks. Overcoming this hurdle, the researchers have successfully devised a technique for fabricating nanoscale quantum sensors directly on the surface of the target material.

To achieve this, the team employed lattice defects called boron vacancies in a two-dimensional hexagonal boron nitride, a thin crystalline material consisting of nitrogen and boron atoms. These boron vacancies, discovered as quantum spin sensors in 2020, act as the quantum sensors in this study.

By delicately peeling off a thin film of hexagonal boron nitride using Scotch tape, the researchers obtained the desired material. They then attached this thin film to a gold wire and bombarded it with a high-speed helium ion beam. This process ejected boron atoms, creating nanoscale boron vacancy spots measuring about 100 nm² each. Within each spot, multiple atom-sized vacancies functioned as tiny magnetic needles. The closer these spots were to each other, the higher the spatial resolution of the sensors. When an electric current flowed through the wire, the team measured the magnetic field at each spot by analyzing the emitted light's intensity in the presence of microwaves. Astonishingly, the measured magnetic field values closely matched the simulated values, affirming the effectiveness of these high-resolution quantum sensors.

One remarkable advantage of these quantum sensors is their ability to detect changes in the spin state even at room temperature, making it convenient to assess local magnetic fields and currents. Additionally, the boron nitride nanofilms adhere to different materials through van der Waals forces, ensuring easy integration of these quantum sensors with various objects.

Sasaki and his team envision applying this technique to explore condensed matter physics and quantum materials further. Sasaki states, " It will enable direct detection of the magnetic field from, for example, peculiar states at edges of graphene and microscopic quantum dots"

The advent of atom-sized quantum sensors is revolutionizing our ability to sense and comprehend microscopic environments, thereby enhancing our understanding of macroscopic properties. These sensors hold immense potential beyond fundamental scientific research. They could be instrumental in imaging the human brain, accurately mapping underground environments, and detecting tectonic shifts and volcanic eruptions. Excitedly, Sasaki and his team anticipate the wide-ranging applications of their nanoscale quantum sensors in the fields of semiconductors, magnetic materials, and superconductors.

Source: University of Tokyo

Cite this article:

Hana M (2023), Precision at the Nanoscale: Unlocking Quantum Sensing on Target, AnaTechmaz, pp.486